Re: [Xen-devel] [PATCH 0/4] ARM: ACPI: ITS: Add ITS Support for ACPI hardware domain

[Julien Grall <julien.grall@xxxxxxx>]

On 10/08/17 13:00, Manish Jaggi wrote:
> Hi Julien,
>
> On 8/10/2017 4:58 PM, Julien Grall wrote:
> > On 10/08/17 12:21, Manish Jaggi wrote:
> > > Hi Julien,
> > >
> > > On 6/21/2017 6:53 PM, Julien Grall wrote:
> > > > Hi Manish,
> > > >
> > > > On 21/06/17 02:01, Manish Jaggi wrote:
> > > > > This patch series adds the support of ITS for ACPI hardware domain.
> > > > > It is tested on staging branch with has ITS v12 patchset by Andre.
> > > > >
> > > > > I have tried to incorporate the review comments on the RFC v1/v2
> > > > > patch.
> > > > > The single patch in RFC is now split into 4 patches.
> > > > I will comment here rather than on each patches.
> > > >
> > > > > Patch1: ARM: ITS: Add translation_id to host_its
> > > > >  Adds translation_id in host_its data structure, which is populated
> > > > > from
> > > > >  translation_id read from firmwar MADT. This value is then programmed
> > > > > into
> > > > >  local MADT created for hardware domain in patch 4.
> > > > I don't see any reason to store value that will only be used for
> > > > generating the MADT which BTW is just a copy for the ITS. Instead we
> > > > should copy over the MADT entries.
> > > There are two approaches,
> > >
> > > If I use the standard API  acpi_table_parse_madt which would iterate
> > > over ACPI_MADT_TYPE_GENERIC_TRANSLATOR entries, I have to maintain the
> > > addr and translation_id in some data structure, to be filled later in
> > > the hwdomain copy of madt generic translator.
> > >
> > > If I don't use the standard API I have to add code to manually parse all
> > > the translator entries.
> > There are a 3rd approach I suggested and ignored... The ITS entries
> > for Dom0 is exactly the same as the host entries.
> Yes, and if not passed properly dom0 wont get device interrupts...
> > So you only need to do a verbatim copy of the entry...
> Can you please check patch 4/2, the translation_id and address are
> passed verbatim, the other values are reserved in
> acpi_madt_generic_translator.
For ACPI, we took the approach to only rewrite what's necessary and give 
the rest to Dom0 as it is. If newer version of ACPI re-used those 
fields, then they will be copied over to Dom0. I don't consider it as an 
issue because the problem would be the same if those fields have an 
important meaning for the platform.
> Could you please detail 3rd approach and how different it is from
> approach 2.
ACPI_MEMCPY(its, host_its, size);

Cheers,

--
Julien Grall

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